The present invention relates to an adsorption process in which a feed stream is introduced into a plurality of adsorbent beds, operated in accordance with an out of phase cycle, to adsorb one or more preferentially adsorbed components contained within a feed stream and thereby produce a product stream. More particularly, the present invention relates to such an adsorption process in which high and low pressure feed streams are introduced into the adsorbent beds to produce high and low pressure product streams.
There are many industrial processes that require feed streams to be pre-treated by adsorption and thereafter to be delivered to the process at two or more pressures. As an example, air separation requires treatment of incoming feed air stream by adsorption beds to remove carbon dioxide and moisture from such feed stream. The treated feed stream can then be fed into the process at high and low operational pressures of distillation columns employed in distilling the treated air.
An example of this can be found in U.S. Pat. No. 4,964,901, in which air is separated by a low temperature rectification process employing higher and lower pressure columns operatively associated with one another by a condenser reboiler. In this process, air is compressed and purified to remove carbon dioxide and water vapor. Thereafter, the air is cooled to a temperature suitable for its rectification and is introduced as feed streams into the higher and lower pressure columns. The higher pressure column serves to separate the air into a nitrogen rich fraction and a crude liquid oxygen column bottoms. The crude liquid oxygen is further refined in the lower pressure column to produce a liquid oxygen column bottoms and a nitrogen rich tower overhead. In order to feed both the high and lower pressure columns with the feed streams, compressed and purified feed air streams are required at the pressure of the higher pressure column and the pressure of the lower pressure column. In order to effectuate the production of such feed streams, incoming air is compressed to the pressure of the lower pressure column and is then divided into two subsidiary streams. One subsidiary stream is further compressed and then purified in a pre-purification unit to form the high pressure feed stream. The other stream, which is at the pressure of the lower pressure column, is purified within a separate pre-purification unit.
In other processes requiring feed air streams at high and low pressures, all of the air is compressed to the pressure of the higher pressure column, pre-purified and then divided. One subsidiary stream is utilized at the higher pressure and the other subsidiary stream is expanded by valve expansion to the lower pressure of the lower pressure column. As can be appreciated, U.S. Pat. No. 4,964,901 is more energy efficient than the aforementioned process because not all of the air is compressed to the higher pressure. The disadvantage of the foregoing process is that two separate pre-purification units are required.
As will be discussed, the present invention provides an adsorption process which is capable of producing product streams at high and low pressures in which only a single unit is required for such purpose.